The invention provides a connection part structure of a combined frame. A connection part is formed by combining a first block body and a second block body, wherein one side of the first block body extends to be provided with a plurality of plate-shaped convex ribs in a protruding mode, and a plurality of longitudinal assembly long grooves and transverse assembly long grooves are defined by the plurality of plate-shaped convex ribs. The second block body and the first block body are assembled in an abutting-against mode, a plurality of assembly groove openings are formed between the first block body and the second block body, and the other side of the second block body extends to be provided with plugging long grooves. Therefore, a plate body is assembled on connection parts in a mode that four corners of the plate body are matched with the connection parts, a square framework is formed by matching the plate body and the assembly long grooves of the first block body in a surrounding mode, another plate is further fixedly connected with the square framework through the assembly groove openings to serve as a back plate, the plate body can be assembled by matching of the plugging long grooves of the second block body to transversely extend the using state of the combined frame, and a combined frame structure for use is formed.